纳米银与表面吸附荧光素的荧光性能的影响

研究了纳米银粒子对表面吸附荧光素(fluorescein,Fl)的荧光性能的影响。Fl溶液中加入纳米银粒子,Fl分子包覆在纳米银粒子表面形成Fl_n-Ag复合物使纳米银相互桥连形成类似网络的结构,且Fl分子吸收峰随着纳米银浓度的增加发生红移。纳米银通过产生的强局域场将能量传输给Fl发光中心,实现了Fl的荧光增强,荧光增强效率随着纳米银浓度的增加具有最大值。较大粒径的纳米银使Fl获得最大荧光增强效率所需浓度较低且最大荧光增强效率值较高。研究结果表明,纳米银与Fl间的能量传输主要由Fl分子附近局域电磁场增强和分子到金属表面无辐射跃迁能量转移过程所决定并与纳米银的浓度、尺寸密切相关。     

Surface enhanced infrared spectral investigation of 2,3-bis(chloromethyl)anthracene-1,4,9,10-tetraone on silver nanoparticles

The size effect of silver nanoparticles on photophysical properties of 2,3-bis(chloromethyl)anthracene-1,4,9,10-tetraone (BCMAT) has been investigated using an IR technique. Silver colloids of different sizes have been prepared by two different methods. Mechanisms for adsorption and complex formation have been elucidated from surface-enhanced infrared absorption spectra. The observation shows that BCMAT is adsorbed on silver nanoparticles through a C = O group and that its orientation is stand-on. Surface enhancement factors have been calculated. As the particles decrease in size their total surface area grows, which leads to the gain in the enhancement factor.     

Controlling SERS intensity by tuning the size and height of a silver nanoparticle array

It is demonstrated that the surface-enhanced Raman scattering (SERS) intensity of R6G molecules adsorbed on a Ag nanoparticle array can be controlled by tuning the size and height of the nanoparticles. A firm Ag nanoparticle array was fabricated on glass substrate by using nanosphere lithography (NSL) combined with reactive ion etching (RIE). Different sizes of Ag nanoparticles were fabricated with seed polystyrene nanospheres ranging from 430 nm to 820 nm in diameter. By depositing different thicknesses of Ag film and lifting off nanospheres from the surface of the substrate, the height of the Ag nanoparticles can be tuned. It is observed that the SERS enhancement factor will increase when the size of the Ag nanoparticles decreases and the deposition thickness of the Ag film increases. An enhancement factor as high as 2×10⁶ can be achieved when the size of the polystyrene nanospheres is 430 nm in diameter and the height of the Ag nanoparticles is 96 nm. By using a confocal Raman mapping technique, we also demonstrate that the intensity of Raman scattering is enhanced due to the local surface plasmon resonance (LSPR) occurring in the Ag nanoparticle array.     

Modelling of optical absorption of silver NP’s produced by UV radiation embedded in mesostructured silica films

Hexagonal mesostructured films containing silver ions were obtained by sol–gel method. Brij 58 was used to produce channels into the film, which house these ions. The films were exposure to UV radiation to produced silver metallic nanoparticles. The presence of the metallic nanoparticles was determined by infrared spectroscopy and optical absorption. Besides, these nanoparticles and core–shell structures of silver–silver oxide nanoparticles were identified by high-resolution transmission electronic microscopy. From these measurements, the obtained size range for silver nanoparticles was 6.1 nm. The absorption spectrum located at 440 nm was modelled and well fitted with the Gans theory considering refractive index higher than the one coming from host matrix. This index is explained because the silver oxide shell modifies the local surrounding medium of the metallic nanoparticles.     

Optical properties and ultrafast electron dynamics in gold–silver alloy and core–shell nanoparticles

Silver and gold are the two most popular metals used for many nanoparticle applications, such as surface enhanced Raman scattering or surface enhanced fluorescence, in which the local field enhancement associated with the excitation of the localized surface-plasmon–polariton resonance (SPR) is exploited. Therefore, tunability of the SPR over a wide energy range is required. For this purpose we have investigated core–shell nanoparticles composed of gold and silver with different shell thicknesses as well as the impact of alloying on these nanoparticles due to a tempering process. The nanoparticles were prepared by subsequent deposition of Au and Ag atoms or vice versa on quartz substrates followed by diffusion and nucleation. Their linear extinction spectra were measured as a function of shell thickness and annealing temperature. It turned out that different gold shell thicknesses on silver cores allow a tuning of the SPR position from 2.79 to 2.05 eV, but interestingly without a significant change on the extinction amplitude. Heating of core–shell nanoparticles up to only 540 K leads to the formation of alloy nanoparticles, accompanied by a back shift of the SPR to 2.60 eV. Calculations performed in quasi-static approximation describe the experimental results quite well and prove the structural assignments of the samples. In additional experiments, we applied the well-established persistent spectral hole burning technique to the alloy nanoparticles in order to determine the ultrafast dephasing time T ₂. We obtained a dephasing time of T ₂=(8.1±1.6) fs, in good agreement with the dephasing time of T _2,∞=8.9 fs, which is already included in the dielectric function of the bulk.     

Synthesis and characterization of silver nanoparticles: effect on phytopathogen <Emphasis Type="Italic">Colletotrichum gloesporioides</Emphasis>

Colloidal silver nanoparticles were synthesized by reducing silver nitrate solutions with glucose, in the presence of gelatin as capping agent. The obtained nanoparticles were characterized by means of UV–Vis spectroscopy, transmission electron microscopy (TEM), and Fourier transform infrared (FTIR) spectroscopy. The response surface methodology (RSM) was also used to determine the influence of the variables on the size of the nanoparticles. The antifungal activity of the silver nanoparticles was evaluated on the phytopathogen Colletotrichum gloesporioides, which causes anthracnose in a wide range of fruits. The UV–Vis spectra indicated the formation of silver nanoparticles preferably spherical and of relatively small size (<20 nm). The above-mentioned was confirmed by TEM, observing a size distribution of 5–24 nm. According to RSM the synthesis variables influenced on the size of the silver nanoparticles. By means of FTIR spectroscopy it was determined that gelatin, through their amide and hydroxyl groups, interacts with nanoparticles preventing their agglomeration. The growth of C. gloesporioides in the presence of silver nanoparticles was significantly delayed in a dose dependent manner.     

Nonlinear optical properties of nanometer-size silver composite azobenzene containing polydiacetylene film

Diacetylene monomer containing p-nitrophenyl azobenzene moiety (NADA) was synthesized. Silver nanoparticles with different concentrations were adulterated in the above polymerized NADA (PNADA) films and the third-order nonlinear optical properties were investigated in detail. UV–vis spectra and transmission electron microscopy were used to confirm the formation of PNADA/Ag nanocomposite films. The silver nanoparticles (average size of 10 nm) were well dispersed in the polymer films. The value of the nonlinear refractive index n ₂ for PNADA films (8.48×10⁻¹⁵ cm²/W) was much higher than that of pure polydiacetylene films. Further, the introduction of silver nanoparticles into the PNADA polymer films led to the further enhancement of nonlinear optical properties. The maximum value of n ₂ for PNADA/Ag nanocomposite films could be 11.6×10⁻¹⁵ cm²/W. This enhancement should be ascribed to the surface plasmon resonance of silver nanoparticles.     

Investigation of resonant properties of metal core–shell nanoparticles using T-matrix calculations

Using T-matrix method, plasmon resonance properties of metal core–shell nanoparticles are systematically investigated. It is shown that dielectric/metal core–shell structure may be excited stronger at resonance than metal/dielectric and hetero-metal ones, but the resonance states are extremely sensible to the layers thickness. For three-layer nanospheres, resonance properties will be dominated by a sub-10 nm silver outermost shell, while only weakened by a silica one. Finally, tiny eccentric distance between the centers of core and shell in eccentric two-layer nanoparticles may fundamentally change the resonance mode of nanoparticles, and results in higher local electrical field enhancement than concentric nanospheres.     

Preparation of triethylamine stabilized silver nanoparticles for low-temperature sintering

In this article, silver nanoparticles were synthesized by chemical reduction from silver nitrate using triethylamine as the protecting and reducing agents simultaneously. The average size of the silver nanoparticles was about 2.10–4.65 nm, which allowed low-temperature sintering of the metal. X-ray diffraction (XRD), thermogravimetric analysis (TGA), and energy dispersive spectrometric (EDS) analysis results indicate that silver nitrate has been converted to silver nanoparticles completely. Using a 20 wt% silver nanoparticles suspension with thermal treatment at 150 °C, silver films with a resistivity of 8.09 × 10⁻⁵ Ω cm have been produced, which is close to the resistivity of bulk silver.     

纳米银粒子对表面吸附罗丹明B的光谱学性质的影响及电解质效应研究

基于贵金属纳米粒子的局域场增强效应,利用透射电子显微镜、紫外-可见分光光度计和荧光分光光度计等分析手段研究了纳米银粒子对表面吸附罗丹明B的光谱学性质的影响以及罗丹明B-纳米银体系中加入电解质离子后,电解质离子与纳米银、染料分子间的相互关系和作用.研究结果表明,当罗丹明B溶液的浓度小于0.6 μmol·L－1时,微量纳米银可使其荧光强度略增加,继续增加纳米银浓度则造成荧光强度下降.当罗丹明B溶液的浓度高于0.6 μmol·L－1时,纳米银总是引起溶液的荧光强度下降.KNO3、KCl、Ca(NO3)2、MgCl2和CaCl2电解质可造成纳米银粒子不同程度的聚集和生长.引起的纳米银粒子的聚集程度关系为:CaCl2>MgCl2>KCl>Ca(NO3)2>KNO3.随着电解质加入量的增加,溶液的荧光强度先下降,而后又逐渐增强,直至达到定值.各电解质对罗丹明B-Ag溶液的荧光强度影响强弱关系为Ca(NO3)2>CaCl2>MgCl2>Cl>KNO3.     

Formation of SERS-active silver structures on the surface of mesoporous silicon

We have optimized the procedure for preparation of nanostructured silver films on the surface of mesoporous silicon (PSi) to use them as active substrates in surface-enhanced Raman scattering (SERS) spectroscopy. The greatest enhancement of the SERS signal was observed for samples obtained when the silver was deposited on PSi from an aqueous AgNO₃ solution with concentration 1⋅10^–2 M over a 10–15 minute period. The detection limit for rhodamine 6G on SERS-active substrates prepared by the optimized procedure was 1⋅10^–10 M. The enhancement factor for the SERS signal on these surfaces was estimated as ≈2⋅10⁸. We have shown that SERS-active substrates based on mesoporous silicon are promising for detection and study of complex organic compounds, in particular tetrapyrrole molecules. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 2, pp. 298–306, March–April, 2009.     

Spatial dependence of the local field enhancement in dielectric shell coated silver nanospheres

The dependence of the local field factor around dielectric shell coated silver nanospheres was investigated by theoretical calculation as a function of the spatial distance. The local field factors in the dielectric shell are sensitive to the distance from particle center and shell thickness. When the shell dielectric constant is greater than that of surrounding medium, the maximum of local field factor at inner surface of the shell red shift and increases nonlinearly with increasing the shell thickness. On the contrary, when shell dielectric constant is less than that of surrounding medium, increasing the shell thickness leads the maximum of local field factor at inner surface blue shifts and decreases nonlinearly. However, with increasing the shell thickness, the maximum of local field factor at exterior surface of the shell always decrease nonlinearly. Furthermore, with increasing shell thickness, all these variations get gentle approach to a constant value when the shell thickness is two times of the core radius. When the core and shell diameter have fixed values, the local field factors in dielectric shell decrease with increasing the distance from particle center, but the peak position is not sensitive to the distance.     

Improved fluorescent assay sensitivity using silver island films: Fluorescein isothiocyanate-labeled albumin as an example

We have studied enhancement of the fluorescence of fluorescein isothiocyanate (FITC), bound to albumin and near an annealed silver island film, as a function of the distance between the protein molecules and the metal. As the intermediate spacer layer between the albumin and the silver substrate, we used multilayer films based on polyelectrolytes. The maximum nine-fold enhancement coefficient for the fluorescence of FITC corresponds to a thickness of the intermediate layer of ≈4 nm, or three layers of the polyelectrolyte. In this case, we observe a significant decrease in the average photoluminescence decay time for the label near the silver film compared with a dielectric medium. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 6, pp. 797–800, November–December, 2006.     

Energy transfer and frequency upconversion in Yb3+–Er3+-doped PbO-GeO2 glass containing silver nanoparticles

We report the infrared-to-visible frequency upconversion in Er³⁺–Yb³⁺-codoped PbO-GeO₂ glass containing silver nanoparticles (NPs). The optical excitation is made with a laser at 980 nm in resonance with the ²F_5/2→²F_7/2 transition of Yb³⁺ ions. Intense emission bands centered at 525, 550, and 662 nm were observed corresponding to Er³⁺ transitions. The simultaneous influence of the Yb³⁺→Er³⁺ energy transfer and the contribution of the intensified local field effect due to the silver NPs give origin to the enhancement of the whole frequency upconversion spectra.     

The activation energy for γ-Fe precipitates inCuFe

The precipitation of the fcc γ-phase of iron has been studied by a systematic series of isothermal and isochronal (0–48 h) heat treatments (300–800°C) on a supersaturated solution ofCuFe containing 3 at% Fe. The optimal conditions (450–600°C) for precipitation of the maximum fraction (90%) of iron attainable within 48 h in the form of γ-Fe have been delineated from analysis of the room temperature spectra. The time dependence for formation of γ-Fe precipitates is well described by the equation for long term annealing. An activation energyE _a ≈0.6 eV for the formation of γ-Fe in Cu is obtained. It indicates short range rather than long range diffusion in theCuFe sample studied.     

Green synthesis of silver nanoparticle by <Emphasis Type="Italic">Penicillium purpurogenum</Emphasis> NPMF: the process and optimization

An eco-friendly microbial method for synthesis of silver colloid solution with antimicrobial activity is developed using a fungal strain of Penicillium purpurogenum NPMF. It is observed that increase in concentration of AgNO₃ increases the formation of silver nanoparticle. At 5 mM concentration highly populated polydispersed nanoparticles form. Furthermore, change in pH of the reaction mixture leads to change in shape and size of silver nanoparticles. At lower pH two peaks are observed in the absorption spectra showing polydispersity of nanoparticles. However, highly monodispersed spherical nanoparticles of 8–10 nm size form with 1 mM AgNO₃ concentration at pH 8. Antimicrobial activity of nanoparticles is demonstrated against pathogenic gram negative bacteria like Escherichia coli and Pseudomonas aeruginosa, and gram positive bacteria like Staphylococcus aureus. The antimicrobial activity of silver nanoparticles obtained at different initial pH show strong dependence on the surface area and shape of the nanoparticles.     

Nanosphere Templated Metallic Grating Assisted Enhanced Fluorescence

In this paper, enhanced fluorescence from a silver film coated nanosphere templated grating is presented. Initially, numerical simulation was performed to determine the plasmon resonance wavelength by varying the thickness of the silver film on top of a monolayer of 400 nm nanospheres. The simulation results are verified experimentally and tested for enhancing fluorescence from fluorescein isothiocyanate whose excitation wavelength closely matches with the plasmon resonance wavelength of the substrate with 100 nm silver film over nanosphere. The 12 times enhancement in the intensity is attributed to the local field enhancement in addition to the excitation of surface plasmon polaritons along the surface.     

A study on the spectral characteristics of surface enhanced Raman scattering based on far‐field extinction and near‐field electromagnetic field intensity of 2D nanostructures

A new solid‐state electrochemical patterning technique was applied to fabrication of high‐resolution silver bowtie antennas and hexagonal arrays. These silver nanofeatures were used to investigate the relation among surface enhanced Raman scattering (SERS) enhancement factor (EF), extinction, local electromagnetic (EM) field maxima of the features. It is found that spectral extinction property or the plasmonic resonance of a given SERS substrate alone is not sufficient for determining optimal EF; the number of points of high local EM field, or ‘hot spots’, and the distribution of those high‐field spots, too, play a role. Copyright © 2014 John Wiley & Sons, Ltd.     

Microwave-assisted rapid extracellular synthesis of stable bio-functionalized silver nanoparticles from guava (<Emphasis Type="Italic">Psidium guajava</Emphasis>) leaf extract

Our research interest centers on microwave-assisted rapid extracellular synthesis of bio-functionalized silver nanoparticles of 26 ± 5 nm from guava (Psidium guajava) leaf extract with control over dimension and composition. The reaction occurs very rapidly as the formation of spherical nanoparticles almost completed within 90 s. The probable pathway of the biosynthesis is suggested. Appearance, crystalline nature, size and shape of nanoparticles are understood by UV–vis (UV–vis spectroscopy), FTIR (fourier transform infrared spectroscopy), XRD (X-ray diffraction), FESEM (field emission scanning electron microscopy) and TEM (transmission electron microscopy) techniques. Microwave-assisted route is selected for the synthesis of silver nanoparticles to carry out the reaction fast, suppress the enzymatic action and to keep the process environmentally clean and green.     

Fluorescence Quenching of 1,4-Dihydroxy-2,3-Dimethyl-9,10-Anthraquinone by Silver Nanoparticles: Size Effect

Size effect of silver nano particles on the photophysical properties of 1,4-dihydroxy-2,3-dimethyl-9,10-anthraquinone (DHDMAQ) have been investigated using optical absorption and fluorescence emission techniques. Silver nanoparticles of different sizes have been prepared by Creighton method using magnetic stirrer and ultrasonic field. Quenching of fluorescence of DHDMAQ has been found to increase with decrease in the size of the silver nanoparticles. Stern–Volmer quenching constants have also been calculated.